I have installed a new kernel on my system which can be found by grub but when I restart I can only select the old kernel. Things I tried in other threds with similar problems didn't help.

sudo update-grub

gives

Generating grub configuration file ...
Found linux image: /boot/vmlinuz-3.15.0-031500rc2-lowlatency
Found initrd image: /boot/initrd.img-3.15.0-031500rc2-lowlatency
Found linux image: /boot/vmlinuz-3.15.0-031500rc2-generic
Found initrd image: /boot/initrd.img-3.15.0-031500rc2-generic
Found linux image: /boot/vmlinuz-3.13.0-24-generic
Found initrd image: /boot/initrd.img-3.13.0-24-generic
Found memtest86+ image: /boot/memtest86+.elf
Found memtest86+ image: /boot/memtest86+.bin
done

However, afer a reboot I can only choose the 3.13 kernel. Any ideas what happened? I I have a full encrypted hard drive so maybe I have overseen something while installing the new kernel to get this work?

The grub config file is

GRUB_DEFAULT=0
GRUB_HIDDEN_TIMEOUT_QUIET=false
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT=""
GRUB_ENABLE_CRYPTODISK=1

Any ideas? Thanks.